Rubber/plastic co-extrusion

ABSTRACT

The present invention provides a non-rusting unitary co-extruded article, which may be used for a variety of purposes, including a seal. The co-extruded article is comprised of at least two dissimilar discrete parts such as a rubber component, referred to herein as the &#34;rubber extrudate,&#34; and a thermoplastic component, referred to herein as the &#34;plastic extrudate.&#34; A particular advantage of the invention is that the rubber extrudate and thermoplastic extrudate are cohesively joined at their interface. By cohesively joined, it is meant that the two extrudates stick together tightly without the necessity of a separate adhesive. Where hardness is desired of the thermoplastic extrudate, ethylene vinyl acetate is generally preferred. Where a seal is desired, the rubber extrudate comprises ethylene propylene diene rubber, which provides a suitable seal. The invention also relates to a method for making the same.

BACKGROUND OF THE INVENTION

Seals, such as, for example, gaskets, are comprised of a flexible softmaterial, typically rubber. The softness and flexibility of the rubberpermits the rubber to conform to the adjacent surface to provide a seal.Suitable rubbers for seals, such as ethylene propylene diene monomerrubbers, are well known. Seals generally require a second rigidmaterial, attached to the rubber, to provide a surface for attaching therubber. Typically, this rigid material has been a metal, such as steel.However, steel has several disadvantages; cost and a propensity to rust.Attempts have been made to substitute the steel rigid material withplastic; plastic provides rigidity at a lower cost and will not rust.However, joining plastic to rubber, as in joining rubber to steel,presents several problems. Joining the plastic to rubber has beenconventionally accomplished by adhesives and/or clips. However, joiningany dissimilar materials with an adhesive often may result in a jointthat may over time fail.

It would be advantageous to have an article containing a rubbercomponent and a plastic component having a continuous strong jointbetween the rubber and plastic, that will not rust.

SUMMARY OF THE INVENTION

The present invention provides a non-rusting unitary co-extrudedarticle, which may be used for a variety of purposes, including a seal.The co-extruded article is comprised of at least two dissimilar discreteparts such as a rubber component., referred to herein as the "rubberextrudate," and a thermoplastic component, referred to herein as the"plastic extrudate." A particular advantage of the invention is that therubber extrudate and thermoplastic extrudate are cohesively joined attheir interface. By cohesively joined, it is meant that the twoextrudates stick together tightly without the necessity of a separateadhesive. Where hardness is desired of the thermoplastic extrudate,ethylene vinyl acetate is generally preferred. Where a seal is desired,the rubber extrudate comprises ethylene propylene diene rubber, whichprovides a suitable seal. The invention also relates to a method formaking the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the seal embodiment of the co-extrudatein use as a door seal;

FIG. 1A is a detailed view of a portion of FIG. 1 on an enlarged scale;

FIG. 2 is a transverse-sectional view of the seal embodiment of theco-extrudate;

FIG. 3 is a perspective view of the die showing the co-extrudate beingextruded;

FIG. 4A is an exploded view of a die face parallel the co-extrudateshowing the front surface of the die face and the front surface of eachdie plate;

FIG. 4B is an exploded view of the die showing the back surface of eachdie plate;

FIG. 5 is a view of the die face of the front die plate;

FIG. 6 is a view of the front surface of the middle die plate;

FIG. 7 is a sectional view taken substantially along the lines 7--7 ofFIG. 5;

FIG. 8 is a sectional view taken substantially along the lines 8--8 ofFIG. 5; and,

FIG. 9 shows the back surface of the rear die plate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is shown in a seal embodiment in use in FIGS. 1and 1A. The present invention provides a co-extruded article 10,comprised of a rubber extrudate 14, and a plastic extrudate 18. Aparticular advantage of the invention is that the rubber extrudate 14and plastic extrudate 18 are cohesively joined at their interface 20.The rubber extrudate 14 has been extruded to contain void 22 running thelength of the rubber extrudate 14. The cohesive interface 20 providesthe advantage of a strong, continuous bond between the two materialswhich does not necessitate adhesives, clips, or the like, and which willnot rust and is resistant to failure at the interface.

The invention has the advantages of providing in a unitary structure theproperties of both plastic and the rubber at the locations where theseproperties are needed. The plastic, which contributes rigidity and formto the article, has several advantages over steel: plastic is lower incost, it doesn't rust, it can take color so as to provide a finishedsurface, it is lighter weight and can be formed to occupy less space.The rubber has superior sealing properties such as conformity at thesealing junction with another member.

In the seal embodiment, where elevated hardness is desired of theplastic extrudate, ethylene vinyl acetate is generally preferred. In thebroader application, this invention may provide a co-extrudate of twodissimilar discrete materials. By dissimilar discrete materials it ismeant materials which upon meeting will not substantially mix and willretain their characteristic properties. The rubber extrudate comprisesethylene propylene diene rubber which provides a suitable seal. Theco-extruded seal exhibits: outstanding toughness, particularly at lowtemperatures; flexibility; resilience; environmental stress crackresistance; excellent ozone resistance; and performance within atemperature range from at least as low as -40° F. to at least as high as200° F. The co-extrudate 10 in the seal embodiment is particularlydesigned for, and is particularly useful as an automobile door seal asshown in FIG. 1. The plastic extrudate 18 is affixed to the rocker panel24 of the car. When the car door 26 is closed the lower interior portionof the door 28 comes in contact with the rubber portion 14 to provide aconformed seal.

In the seal embodiment, the rubber is typically extruded in a "profiled"form to provide a rubber extrudate having a longitudinal void 22 asshown in FIG. 2. This will enhance its sealing properties in that itprovides improved flexibility and compressibility to the rubberextrudate 14 as it abuts against the car door 26.

The present invention also relates to a method for co-extruding twodissimilar materials like rubber, such as, for example, ethylenepropylene diene monomer (EPDM) and a plastic, such as, for example,ethylene vinyl acetate (EVA). The invention also relates to an apparatusand process for forming the co-extrudate involving the use of twoextruders, one extruder for each material, such as a rubber extruder anda plastic extruder. The extruders and the die are set so that the rubberand plastic meet right before the die face where they are extruded. Themethod and apparatus for extruding will be described presently.

Materials The Plastic Extrudate

The plastic extrudate 18 may be made from any of a variety ofthermoplastic materials including, for example,Poly-2,6-dimethyl-1,4-phenylene ether (available under the trade name"Vestoran" from Huls), or ethylene vinyl acetate, "EVA." The selectionof the type of plastic depends on the end use of the co-extrudate andthe desired properties of the plastic extrudate. Where a relatively hardmaterial is desired, that is it is desired that the plastic have adurometer value of at least 95 Shore A, EVA is preferred. While manytypes of EVA may be used, good results have been obtained using "Elvax770" available from Dupont. While the precise formulation of Elvax 770is proprietary, the Elvax 770 contains about 9.5% moles of vinylacetate, and has a melt index of about 0.8 dg/min. The EVA startingmaterial may be pelletized, flaked or in other forms. It should also beunderstood that commercially available EVA may contain additives, suchas initiators and accelerators. In the seal embodiment, the plastic istypically extruded to provide a solid plastic extrudate 18, as shown inFIGS. 1A and 3, and in cross section in FIG. 2.

The Rubber Extrudate

A variety of rubbers including, for example, ethylene propylene dienemonomer, "EPDM," silicone or an EPDM/silicone blend or mixtures thereof,may be used to produce the rubber extrudate 14. The selection of thetype of rubber depends upon the end of use of the co-extrudate.Typically, the rubber should have a shore A durometer value of fromabout 40 to about 90. Where the end use of the co-extrudate is a seal,which may require, for example, a soft rubber having a durometer ofabout 50, good results have been obtained using ethylene propylene dienemonomer rubber, "EPDM" rubber. EPDM is available commercially and goodresults have been obtained using a blend of EPsyn® P597 and EPsyn® 5508available from Copolymer Company. EPsyn® P597 contains 61% ethylene and35.9% propylene; the diene, which is ethyl diene norborene, is presentin about 3.1%. The EPsyn® is an oil extended rubber, that is, 100 phr ofnaphthenic oil has been added to the rubber. EPsyn® 5508 contains 69%ethylene and 27.0% propylene. The diene, which is ethyl diene norborene,is present in the amount of about 4.0%. In the blended EPDM, the EPsyn®P597 is present in an amount of from about 10% to about 90%, preferably50% of the total amount of rubber amount; while the EPsyn® 5508 ispresent in an amount of from about 10% to about 90%, preferably 50% ofthe total amount of rubber. The addition of the oil extended rubber,such as the EPsyn® P597, will provide a softer rubber extrudate.

Carbon Black

Carbon black is added to the rubber, not only as a filler andreinforcer, but also to aid in rendering the rubber sensitive tomicrowave radiation. In this manner, the rubber extrudate portion of theco-extrudate may be selectively heated by microwave radiation tofinalize the curing of the rubber without adversely affecting theplastic portion of the extrudate. While generally any type of carbonblack can be used, good results have been obtained using GPF N-650carbon black, available under the trade name "Continex N-650" fromContinental Carbon Company or "Statex GH N-650" from Columbian. Thecarbon black may be added in an amount from about 50 phr to about 250phr, preferably about 100 phr to about 160 phr, more preferably about125 phr.

Various other additives, discussed subsequently, are added to the rubberto provide the rubber formulation that becomes the rubber extrudate.

Other Ingredients

Curing agents are necessary for the rubber to cure. A variety of thecommercially available curing agents may be used, including, forexample, peroxides and sulfur. Sulfur is preferred where the rubber isEPDM, particularly where EPDM is coextruded with EVA. However, when theplastic extrudate is poly-2,6-dimethyl-1,4-phenylene ether, it ispreferred that peroxide be used to cure the EPDM. Generally peroxide isused in an amount from about 2 to about 20 phr, preferably about 6 to 8phr, preferably about 7 phr. Sulfur is used as a curing agent in anamount from about 0.1 to about 20 phr, preferably about 0.5 phr to about3 phr, preferably about 0.7 phr.

While curing of the rubber can be accomplished in rubber having a highpercentage of sulfur, the time required is too long to be economical andthe properties of the cured rubber are less preferred. Accordingly, acure accelerator is preferred. There are a considerable number of cureaccelerators known in the rubber formulation art which may be suitablefor addition to the rubber. Suitable organic accelerators include, forexample, tetramethyl thiuram disulfide, zinc dibutyl dithiocarbamate,2-mercapto benzothianzole (1.5%), dipenthamethylene thiuram, zincdimethyldithiocarbamate and mixtures thereof. Suitable inorganicaccelerators, such as, for example, calcium oxide, magnesium oxide, leadoxide and mixtures thereof, may also be used. Generally, a cureaccelerator is added in an amount from about 0.5 phr to about 6 phr,preferably 2.5 phr.

Good results have been obtained using a combination of the followingaccelerators: tetramethyl thiuram disulfide, available under the tradename "Methyl Tuads" from R. T. Vanderbilt Co., in an amount from about0.5 phr to about 1 phr, preferably about 0.80 phr; zincdibutyldithiocarbamate, available under the trade name "Butyl Zimate"from R. T. Vanderbilt Co., in an amount from about 0.5 phr to about 3phr, preferably about 0.5 phr, dipenthamethylene thiuram, availableunder the trade name "Tetrone A" from Dupont, in an amount from about0.5 phr to about 1 phr, preferably about 1 phr, zincdimethyldithiocarbamate, available in a 75% active dispersion from RheinChemie, under the trade name "Methyl Zimate," in an amount of 0.5 phr to1 phr, preferably about 0.8 phr; 2-mercaptobenzothiazole, availableunder the trade name "MBT" from Uniroyal, in an amount from about 1 phrto about 3 phr, preferably about 1.5 phr, and calcium oxide, used in a90% active dispersion under the trade name "Elastocal 90," fromElastochem Incorporated in an amount from about 8 phr to about 15.00phr, preferably about 10 phr.

The activation of curing agents, such as sulfur, are typically enhancedby, for example, zinc oxide, and stearic acid and mixtures thereof. An85% active zinc oxide dispersion, available under the trade name "ZicStick 85" from Rhein Chemie, may be used in the amount from about 0 phrto about 40 phr, preferably 5 phr to about 6 phr, more preferably about5.75 phr.

Although optional, there are a great number of plasticizers andprocessing aids known in the rubber formulation art, which may besuitable for addition to the rubber. The selection of plasticizers andprocessing aids depends on the desired property of the rubber,particularly before it is cured. Plasticizers and processing aids areadded to the rubber formulation to increase the incorporation ofingredients during mixing, promote the flow of the rubber, and tofacilitate processing.

Suitable plasticizers include paraffinic oils, naphthenic oils, aromaticoils and mixtures thereof.

Good results have been obtained from using a paraffinic oil of highmolecular weight, available under the trade name "Sunpar 2280" fromSunpar Company. The formulation of the Sunpar 2280 is proprietary; ithas a molecular weight from about 600 grams/mole to over 700 grams/mole.The paraffinic oil is generally added to the rubber formulation in anamount from about 0 phr to about 200 phr, preferably 50 phr to about 100phr, preferably about 75 phr.

Suitable processing aids include, for example, calcium stearate,polyethylene glycol, hydrocarbon resins, fluorochemical alcohols calciumcarbonate, or mixtures thereof.

Good results have been obtained using both calcium stearate in an amountfrom about 1 phr to about 5 phr, preferably about 3 phr, andpolyethylene glycol, in an amount from about 2 phr to about 4 phr,preferably about 2 phr. The calcium stearate improves the stability ofthe uncured rubber, and the polyethylene glycol improves the flow of therubber through the die.

In addition, the rubber or plastic extrusion may contain optionalingredients such as colorants, dyes, fungicides and fillers. Colorantsmust be non-polar so as not to be affected by microwave radiation.

Forming the Product

The co-extrudate 10 of the soft rubber extrudate 14 and the rigidplastic extrudate 18 is made using two extrusion machines, a rubberextruder 40 and a plastic extruder 42 as shown FIG. 3. The rubberextruder 40, preferably is a 31/2 inch diameter Davis Standard extruderwhich is a "cold feed" tuber; i.e., the rubber, which is fed in strips,is room temperature. The rubber extruder is of conventional design andhas a barrel (not shown) which has four heating zones. The four barrelzones are set at temperatures between 150° F. and 170° F. to control thetemperature of the rubber during extrusion in a well known manner. Therubber extruder 40 is aligned at 90° to the extrusion line.

The plastic extruder 42 is aligned with the extrusion line "L."

The plastic extruder 42 is a 31/2 inch diameter NRM extruder which isoperated in a conventional manner. The plastic is fed into a hopper (notshown), typically in a pelletized form. If desired, color additives,which come in a variety of forms, are mixed in appropriate ratios withthe plastic before being placed into the hopper. The barrel (not shown)of the plastic extruder 42 is divided into five zones. The temperatureof each zone can vary from 200° F. to 400° F. Conventional means such asa breaker plate and three screen packs (not shown) may be placed beforethe die 50 to screen out foreign objects in a well known manner.

While either extruder could be equipped with the die that forms theco-extrudate, good results have been obtained using a die 50 affixed tothe plastic extruder 42. The die 50 is mounted by conventional means(not shown) on the plastic extruder 42. The rubber extruder 40 is fittedwith an adaptor 46 comprised of pipes and elbows through which extrudedrubber enters and is carried to the die 50. As shown in FIGS. 3-9, thedie 50 is comprised of three die plates 52, 54, 56. The rear die plate56 abuts the extruder 42 and has rear surface 58 and front surface 60.The rear surface 58 has a concave surface 62 for receipt of the plastic.The rear surface 58 has a further concavity 63 surrounding die opening64 which opening generally conforms to the configuration of the plasticto be extruded.

The rear die plate 56 has two openings therethrough 65 for the two bolts67. Bolts 67 affix the rear die plate 56 to middle die plate 54 and tofront die plate 52. The middle die plate 54, has front surface 66 andrear surface 68. Middle die plate 54 has two drilled holes 69 to receivebolts 67. The rear surface 68 abuts the front surface 60 of the rear dieplate. The rear surface 68 has an opening 70 extending therefrom throughto the front surface 66 and generally conforming in configuration to theplastic to be extruded and which opening is aligned with opening 64. Thefront surface 66 of the middle die plate 54 has a "J" shaped slot 72 forreceipt of the rubber. The "J" shaped slot 72 also has mounted therein acore 74 which extends perpendicularly away from the plane of the middledie plate 54. The core 74 conforms to the shape of the void/bulb 22 inthe rubber extrudate 14. Middle plate 54 has three openings therethroughfor bolts 75. Bolts 75 affix the middle die plate 54 to the front dieplate 52. Middle plate 54 has an annular alignment rib 77.

The front die plate 52 has a rear surface 76 which abuts the frontsurface 66 of the middle die plate 54. Front die plate 52 which has anannular alignment rib 77a. Front die plate also has a front surface 78.Front die plate 52 has three threaded holes therethrough 79 to receivebolts 75 and two threaded holes 81 to receive bolts 67. The front dieplate 52 has an extrusion opening 80 extending therethrough whichconforms in shape to the final shape of the co-extrudate 10. Theextrusion opening 80 is a single orifice which has two segments 82, 84.One segment 82 conforms in shape to the plastic and is aligned with theopenings 64, 70. The second segment 84 conforms in shape to the rubberto be extruded and such segment communicates with the j slot 72. Thecore 74 projects through the second segment 84 to define an annularconfiguration that is the void 22 for the rubber. Segments 82 and 84 arepositioned to extrude a single unitary co-extrudate 10 having a cohesiveinterface.

Front surface 78 also has a perpendicular threaded bore 86 for receiptof the threaded shaft 88 which extends through front die plate 52 and isaligned with shaft 90, in middle die plate 54. Shaft 90 interconnectswith radial shaft 92 located within the middle of die plate 54. Radialshaft 92 interconnects to bore 94 which extends through the core 74. Thefront surface 78 also has a blind threaded bore 96 for receipt of aconventional thermocouple and/or conventional heating device for heatingthe front die plate 52. Also mounted on the front surface 78 of thefront die plate 52 are shapers 98 which may be positioned to shape theco-extrudate as it is being extruded. The rear surface has an opening100 to receive rubber connection of adaptor 46.

Thus, the plastic extruded from extruder 42 encounters the rear surfaceof rear die plate 58. The rear surface of the die 50 has a concavesurface 62 surrounding a steeper concave surface 63 which surrounds thedie opening 64. This streamlining prevents the plastic from hitting deadspots and becoming stagnant, and allows for proper flow of the plastic.The plastic enters the die through opening 64. The plastic proceedsthrough openings 64 and 70 through segment 82 of the front die opening80. The rubber extruded from rubber extruder 40 enters and is carried byadaptor 46 to enter opening 100 on the front surface 78 of the die 50.The rubber enters the J shaped slot 72 where it fills the slot 72 andsurrounds the core 74. The rubber is then extruded back along the samedirection which it entered. The rubber and plastic are physicallyseparated until just before the rear surface 76 of the front die plate52. The two materials are then co-extruded through orifice 80 of dieplate 52. The rubber, which begins curing shortly before enteringorifice 80, cross links with the plastic to provide a cohesive interface20. Air, supplied from the bore 94 at the end of the core 74, is forcedinto the bulb, that is, void 22 of the rubber extrudate 14 to preventthe bulb profile from collapsing and loosing its shape. The shapers 98may be positioned to gently shape the warm co-extrudate 10. Portions ofthe front die plate 52, may be heated by the use of a conventionalheating means inserted through bore 96.

The co-extrudate 10, after it comes out of the die 50, is placed onto aconveyor of a microwave unit. The belt on the conveyor movesapproximately 29 feet per minute. The air inside the microwave is set atapproximately 145° F. to about 150° F., to heat the exterior of theco-extrudate, particularly the rubber extrudate. The air should notexceed 150° F. since the plastic component would tend to lose its shapeif the temperature was any higher than 150° F. The co-extrudate 10 isexposed to microwave radiation which selectively heats the rubberextrudate and further cures the rubber. Since the plastic is notaffected by the microwave radiation, it is not heated beyond the ambientair temperature of the microwave.

After the co-extrudate 10 is exposed to the microwave radiation,coatings may, optionally, be applied using conventional equipment, suchas a spray coating booth. Thereafter, the co-extrudate is conveyed to ahot air oven. While on the conveyor to the hot air oven, air chillersand/or a water spray are used to selectively cool the plastic extrudate;generally this cooling enables the plastic component to maintain itsshape through the rest of the process.

The hot air oven is used to cure the optional coating, and also tofinish curing the rubber. The oven must be kept at low temperatures, ator below about 200° F. to avoid melting the plastic extrudate. Theco-extrudate is maintained in the hot air oven for about one minute.

Next, a puller conveyor is used to pull the co-extrudate from the hotair oven to water cooling tanks under uniform tension. The water coolingtanks have conveyors which transport the co-extrudate through water,which is also sprayed onto the part. At this point, it is possible toshape the plastic before it completely cools. Rollers can be used toshape the plastic extrudate. After the co-extrudate leaves the coolingtank, it can either be cut to length or have secondary operations, suchas punching or notching performed. Thereafter, further modification maybe done by the customer.

Example 1

A co-extrudate according to the present invention was prepared asfollows. The rubber formulation was prepared by adding the followingingredients and mixing for about 5.5 minutes at a final temperature ofabout 245° F.

    ______________________________________                                        Rubber Formulation                                                            Material                100 RHC  KG                                           ______________________________________                                        1)  Ethylene Propylene Diene Monomer                                                                      98.00    42.18                                        (Diene ENB) 100 phr Naphthenic Oil                                            EPsyn ® P597, from Copolymer Co.                                      2)  Ethylene Propylene Diene Monomer                                                                      52.00    22.23                                        (Diene ENB) EPsyn ® 5508, from                                            Copolymer Co.                                                             3)  Carbon Black (N-650), from Continental                                                                125.00   53.98                                    4)  Paraffinic Oil (plasticizer)                                                                          75.00    32.21                                        Sunpar 2280, from Sunpar Co.                                              5)  85% Active Zinc Oxide Dispersion                                                                      5.75     2.49                                         (activator) Zic Stick 85, from                                                Rhein Chemical                                                            6)  Calcium Stearate (processing aid)                                                                     3.00     1.32                                         from Harwick Chemical Co.                                                 7)  Polyethylene Glycol (processing aid)                                                                  2.00     0.86                                         Carbowax PEG 3350 from Harwick                                                Chemical                                                                  8)  2-Mercapto Benzothiazole (accelerator)                                                                1.50     0.64                                         MBT, from Uniroyal                                                        9)  Sulfur (curing agent) from                                                                            0.70     0.32                                         Harwick Chemical Co.                                                      10) Zinc Dibutyl Dithiocarbamate                                                                          0.50     0.23                                         (accelerator) butyl zimate from                                               R. T. Vanderbilt Co.                                                          Dipenthamethylene Thiuram (accelerator)                                                               1.00     0.45                                         Tetrone A Dupont                                                          12) 90% Active Calcium Oxide Dispersion                                                                   10.00    4.31                                         (accelerator) Elastocal 90, from                                              Elastochem                                                                13) Tetramethyl Thiuram Disulfide                                                                         0.80     0.36                                         (accelerator) Methyl Tuads, from                                              R. T. Vanderbilt Co.                                                      14) 75% Active Methyl Zimate Dispersion                                                                   0.80     0.36                                         in Ethylene/Propylene Rubber                                                  (accelerator) from Rhein Chemical                                             Total                   376.05   161.94                                   ______________________________________                                    

The amount of the rubber ingredients varied within 0.07 kilograms. Afterthe rubber formulation was thoroughly mixed, the rubber was cooled toroom temperature and cut into strips.

The rubber was then fed into the Davis Standard Extruder according tothe method outlined above. The ethylene vinyl acetate was fed into thehopper of the NRM extruder in a pelletized form with 0.5% of EV-436Black colorant. The rheostat on the plastic extruder was set to 2.8° andthe temperatures in the five barrel zones were as follows: the rear zone(zone 1), nearest at the hopper, was set at 250° F.; the rear centerzone (zone 2), was set at 300° F.; the center zone (zone 3), was set at300° F.; the front center zone (zone 4), was set at 320° F.; and thefront zone (zone 5), was set at 330° F. The die head and adapter was setat 350° F. The rheostat on the rubber extruder was set to 1.6. Therubber extruder was set at 160° for the rear, center and front barrelzones. The fourth zone, the zone where the rubber enters the adaptor wasset at 180° F. The co-extrudate 10 was produced as outlined above. Themicrowave generator 1 was set at 3.8 kilowatts, generator 2 was set at4.0 kilowatts, and generator 3 was set at 4.0 kilowatts. The support airwithin the microwave was 140° F. The hot air oven was set to roomtemperature. Samples were taken from one extrusion run using an averageof 3 batches of material. The results are provided in Table I.

                  TABLE I                                                         ______________________________________                                        Rubber/Plastic Extrusion                                                      Results of Example 1                                                                              ASTM                                                      Obtained Physical Properties                                                                      Spec.   EPDM     EVA                                      ______________________________________                                        Unaged:                                                                       Durometer, Shore A  D-2240  52       95                                       Tensile, MPa        D-412   12.4     --                                                           D-638   --       20.05                                    Elongation, %       D-412   640      --                                                           D-638   --       800                                      Flexural Modulus, MPa                                                                             D-790   --       11                                       Compression Set--22 Hours @ 70° C.:                                    % Set               D-395   45       80                                       Ovenaged--70 Hours @ 100° C.:                                          Tensile, % Change   D-573   -10.0    --                                       Elongation, % Change        -10.0    --                                       Durometer, Points, Change   +4       --                                       Vicat Softening Temp. °C.                                                                  D-1525  --       80                                       Ozone Resistance--70 Hours @                                                  100 pphm @ 38° C.                                                      Rating              D-1171  No       No                                                                   Cracks   Cracks                                   Brittleness @ -40° C.                                                                      D-2137  Pass     --                                                           D-746   --       Pass                                     ______________________________________                                         -- denotes data is not applicable.                                       

The results in Table I are generally consistent with average values,recited in Table II, obtained from testing several different batches ofEVA/EPDM co-extrudate.

                  TABLE II                                                        ______________________________________                                        Rubber/Plastic Co-Extrudate                                                   Average Values                                                                                    ASTM                                                      Typical Physical Properties                                                                       Spec.   EPDM     EVA                                      ______________________________________                                        Unaged:                                                                       Durometer, Shore A  D-2240  50       98                                       Tensile, MPa        D-412   11.0     --                                                           D-638   --       19.0                                     Elongation, %       D-412   550      --                                                           D-638   --       650                                      Flexural Modulus, MPa                                                                             D-790   --       110                                      Compression Set--22 Hours @ 70° C.:                                    % Set               D-395   21       84                                       Ovenaged--70 Hours @ 100° C.:                                          Tensile, % Change   D-573   -10.0    --                                       Elongation, % Change        -25.0    --                                       Durometer, Points, Change   +5       --                                       Vicat Softening Temp.°C.                                                                   D-1525  --       80                                       Ozone Resistance--70 Hours @                                                  100 pphm @ 38° C.                                                      Rating              D-1171  No       No                                                                   Cracks   Cracks                                   Brittleness @ -40° C.                                                                      D-2137  Pass     --                                                           D-746   --       Pass                                     ______________________________________                                         -- denotes data is not applicable.                                       

As can be seen from Tables I and II, the co-extrudate demonstratesexcellent ozone resistance, heat resistance and excellent flexibility,even at cold temperatures.

While a preferred embodiment of the invention has been disclosed indetail, along with certain alternative constructions and arrangements,the present invention is not to be considered limited to the preciseconstructions disclosed herein. Various adaptations, modifications anduses of the invention may occur to those skilled in the art to which theinvention relates, and the invention is to cover all such adaptations,modifications and uses falling within the spirit and scope of thefollowing claims.

What is claimed is:
 1. A unitary co-extrudate article, comprising:arubber extrudate segment, said rubber extrudate segment passing throughheating zones of a rubber extrudate extrusion machine having settemperatures between 150° F. and 175° F.; a plastic extrudate segment,said plastic extrudate segment passing through heating zones of aplastic extrudate extrusion machine having set temperatures between 200°F. and 400° F.; and a continuous cohesive cross-linked interface formedat a surface of interaction between said rubber extrudate segment andsaid plastic extrudate segment, said interface being formed as saidrubber extrudate segment and said plastic extrudate segment areco-extruded through an orifice of a common die plate to form the unitaryco-extrudate article, and wherein the article is shaped as saidsegments, cross-linked at said interface, exit through the orifice ofthe common die plate.
 2. A unitary co-extrudate article as recited inclaim 1, wherein said rubber extrudate segment comprises ethylenepropylene diene rubber.
 3. A unitary co-extrudate article as recited inclaim 1, wherein said rubber extrudate segment comprises a mixture of anethylene propylene diene rubber and an oil extended ethylene propylenediene rubber.
 4. A unitary co-extrudate article as recited in claim 1,wherein said rubber extrudate segment comprises carbon black.
 5. Aunitary co-extrudate article as recited in claim 1, wherein said plasticextrudate segment comprises ethylene acetate.
 6. A unitary co-extrudatearticle as recited in claim 1, wherein said rubber extrudate segmentcomprises a mixture of ethylene propylene diene rubber and oil extendedethylene propylene diene rubber, a sulfur curing agent, and a cureaccelerator, and wherein said plastic extrudate segment comprisesethylene vinyl acetate.